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.TH "BTRFS-CHECK" "8" "Oct 28, 2024" "6.6.3" "BTRFS"
.SH NAME
btrfs-check \- check or repair a btrfs filesystem
.SH SYNOPSIS
.sp
\fBbtrfs check\fP [options] <device>
.SH DESCRIPTION
.sp
The filesystem checker is used to verify structural integrity of a filesystem
and attempt to repair it if requested.  It is recommended to unmount the
filesystem prior to running the check, but it is possible to start checking a
mounted filesystem (see \fI\%\-\-force\fP).
.sp
By default, \fBbtrfs check\fP will not modify the device but you can reaffirm that
by the option \fI\-\-readonly\fP\&.
.sp
\fBbtrfsck\fP is an alias of \fBbtrfs check\fP command and is now deprecated.
.sp
\fBWARNING:\fP
.INDENT 0.0
.INDENT 3.5
Do not use \fI\-\-repair\fP unless you are advised to do so by a developer
or an experienced user, and then only after having accepted that no \fIfsck\fP
successfully repair all types of filesystem corruption. E.g. some other software
or hardware bugs can fatally damage a volume.
.UNINDENT
.UNINDENT
.sp
The structural integrity check verifies if internal filesystem objects or
data structures satisfy the constraints, point to the right objects or are
correctly connected together.
.sp
There are several cross checks that can detect wrong reference counts of shared
extents, backreferences, missing extents of inodes, directory and inode
connectivity etc.
.sp
The amount of memory required can be high, depending on the size of the
filesystem, similarly the run time. Check the modes that can also affect that.
.SH SAFE OR ADVISORY OPTIONS
.INDENT 0.0
.TP
.B \-b|\-\-backup
use the first valid set of backup roots stored in the superblock
.sp
This can be combined with \fI\-\-super\fP if some of the superblocks are damaged.
.UNINDENT
.INDENT 0.0
.TP
.B  \-\-check\-data\-csum
verify checksums of data blocks
.sp
This expects that the filesystem is otherwise OK, and is basically an offline
\fIscrub\fP that does not repair data from spare copies.
.TP
.BI \-\-chunk\-root \ <bytenr>
use the given offset \fIbytenr\fP for the chunk tree root
.UNINDENT
.INDENT 0.0
.TP
.B \-E|\-\-subvol\-extents <subvolid>
show extent state for the given subvolume
.UNINDENT
.INDENT 0.0
.TP
.BI \-\-mode \ <MODE>
select mode of operation regarding memory and IO
.sp
The \fIMODE\fP can be one of:
.INDENT 7.0
.TP
.B original
The metadata are read into memory and verified, thus the requirements are high
on large filesystems and can even lead to out\-of\-memory conditions.  The
possible workaround is to export the block device over network to a machine
with enough memory.
.TP
.B lowmem
This mode is supposed to address the high memory consumption at the cost of
increased IO when it needs to re\-read blocks.  This may increase run time.
.UNINDENT
.UNINDENT
.INDENT 0.0
.TP
.B \-p|\-\-progress
indicate progress at various checking phases
.TP
.B \-Q|\-\-qgroup\-report
verify qgroup accounting and compare against filesystem accounting
.TP
.B \-r|\-\-tree\-root <bytenr>
use the given offset \(aqbytenr\(aq for the tree root
.UNINDENT
.INDENT 0.0
.TP
.B  \-\-readonly
(default)
run in read\-only mode, this option exists to calm potential panic when users
are going to run the checker
.UNINDENT
.INDENT 0.0
.TP
.B \-s|\-\-super <N>
use Nth superblock copy, valid values are 0, 1 or 2 if the
respective superblock offset is within the device size
.sp
This can be used to use a different starting point if some of the primary
superblock is damaged.
.TP
.B \-\-clear\-space\-cache v1|v2
completely remove the free space cache of the given version
.sp
See also the \fIclear_cache\fP mount option.
.sp
\fBWARNING:\fP
.INDENT 7.0
.INDENT 3.5
This option is deprecated, please use \fIbtrfs rescue clear\-space\-cache\fP
instead, this option would be removed in the future eventually.
.UNINDENT
.UNINDENT
.UNINDENT
.SH DANGEROUS OPTIONS
.INDENT 0.0
.TP
.B  \-\-repair
enable the repair mode and attempt to fix problems where possible
.sp
\fBNOTE:\fP
.INDENT 7.0
.INDENT 3.5
There\(aqs a warning and 10 second delay when this option is run without
\fI\-\-force\fP to give users a chance to think twice before running repair, the
warnings in documentation have shown to be insufficient.
.UNINDENT
.UNINDENT
.TP
.B  \-\-init\-csum\-tree
create a new checksum tree and recalculate checksums in all files
.sp
\fBWARNING:\fP
.INDENT 7.0
.INDENT 3.5
Do not blindly use this option to fix checksum mismatch problems.
.UNINDENT
.UNINDENT
.TP
.B  \-\-init\-extent\-tree
build the extent tree from scratch
.sp
\fBWARNING:\fP
.INDENT 7.0
.INDENT 3.5
Do not use unless you know what you\(aqre doing.
.UNINDENT
.UNINDENT
.UNINDENT
.INDENT 0.0
.TP
.B  \-\-force
allow work on a mounted filesystem and skip mount checks. Note that
this should work fine on a quiescent or read\-only mounted filesystem
but may crash if the device is changed externally, e.g. by the kernel
module.
.sp
\fBNOTE:\fP
.INDENT 7.0
.INDENT 3.5
It is possible to run with \-\-repair but on a mounted filesystem
that will most likely lead to a corruption unless the filesystem
is in a quiescent state which may not be possible to guarantee.
.UNINDENT
.UNINDENT
.sp
This option also skips the delay and warning in the repair mode (see
\fI\-\-repair\fP).
.UNINDENT
.SH DEPRECATED OR MOVED OPTIONS
.INDENT 0.0
.TP
.B  \-\-clear\-ino\-cache
(removed: 6.7)
.sp
remove leftover items pertaining to the deprecated \fIinode cache\fP feature,
please use \fI\%btrfs rescue clear\-ino\-cache\fP
instead
.UNINDENT
.SH EXIT STATUS
.sp
\fBbtrfs check\fP returns a zero exit status if it succeeds. Non zero is
returned in case of failure.
.SH AVAILABILITY
.sp
\fBbtrfs\fP is part of btrfs\-progs.  Please refer to the documentation at
\X'tty: link https://btrfs.readthedocs.io'\fI\%https://btrfs.readthedocs.io\fP\X'tty: link'\&.
.SH SEE ALSO
.sp
\fI\%mkfs.btrfs(8)\fP,
\fI\%btrfs\-scrub(8)\fP,
\fI\%btrfs\-rescue(8)\fP
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